High-speed small boats are used in a variety of applications and are particularly useful in military operations, and search and rescue operations. When fast-moving small watercraft encounter even moderately disturbed water, the passengers are subjected to significant forces. At high-speed, in waves of any appreciable size, small watercraft tend to be subjected to rapid and simultaneous vertical and horizontal acceleration and deceleration.
When a boat moving at high speed impacts the crest of a wave, the boat tends to simultaneously pitch upwards and decelerate, and when it passes over or through the crest and encounters the trough, the boat tends to pitch downwards and accelerate. At high speed, each pitching and acceleration/deceleration cycle may be measured in seconds, such that passengers are subjected to rapid and extreme acceleration and deceleration and the associated shock, which is commonly quantified in terms of multiples of g, a “g” being a unit of acceleration equivalent to that exerted by the earth's gravitational field at the surface of the earth. The term g-force is also often used, but it is commonly understood to mean a relatively long-term acceleration. A short-term acceleration is usually called a shock and is also quantified in terms of g.
Human tolerances for shock and g-force depend on the magnitude of the acceleration, the length of time it is applied, the direction in which it acts, the location of application, and the posture of the body. When vibration is experienced, relatively low peak g levels can be severely damaging if they are at the resonance frequency of organs and connective tissues. In high-speed watercraft, with the passengers sitting in a conventional generally upright position, which is typically required, particularly with respect to the helmsperson and any others charged with watchkeeping, upward acceleration of the watercraft is experienced as a compressive force to an individual's spine and rapid deceleration tends to throw an individual forward.
Shock absorbing systems for high-speed boats are known. For example, U.S. Pat. No. 6,786,172 (Loffler—Shock absorbing boat) discloses a horizontal base for supporting a steering station that that is hingedly connected to the transom to pivot about a horizontal axis. The base is supported by spring bias means connected to the hull.
Impact attenuation systems for aircraft seats are also known, as disclosed in: U.S. Pat. No. 4,349,167 (Reilly—Crash load attenuating passenger seat); U.S. Pat. No. 4,523,730 (Martin—Energy-absorbing seat arrangement); U.S. Pat. No. 4,911,381 (Cannon et al.—Energy absorbing leg assembly for aircraft passenger seats); U.S. Pat. No. 5,125,598 (Fox—Pivoting energy attenuating seat); and U.S. Pat. No. 5,152,578—Kiguchi—Leg structure of seat for absorbing impact energy.
Other seat suspension systems are also known, as disclosed in: U.S. Pat. No. 5,657,950 (Han et al.—Backward-leaning-movement seat leg structure); U.S. patent application Ser. No. 10/907,931 (App.) (Barackman et al.—Adjustable attenuation system for a space re-entry vehicle seat); U.S. Pat. No. 3,572,828 (Lehner—Seat for vehicle preferably agricultural vehicle); U.S. Pat. No. 3,994,469 (Swenson et al.—Seat suspension including improved damping means); and U.S. Pat. No. 4,047,759 (Koscinski—Compact seat suspension for lift truck).